Machining center in which tool holders have a multiple coupling with a cover

ABSTRACT

A machining center has machine tools which each have a working space for machining workpieces  21 , a clamping station  18  in which workpieces  21  to be machined are clamped into workpiece holders  19 , and a loading device which transports the workpiece holders  19  between the clamping station  18  and the working space of at least one machine tool. A multiple coupling  70  for transferring fluidic energy, which is selectably docked in the clamping station  18 , is provided on the workpiece holder  19  (FIG.  5 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a machining center having a number ofmachine tools which each have a working space for machining workpieces,a clamping station in which workpieces to be machined are clamped intoworkpiece holders, and a loading device which transports the workpieceholders between the clamping station and the working space of at leastone machine tool.

2. Related Prior Art

A machining center of this kind is known from DE 195 16 849 A1.

In the known machining center, machine tools are arranged next to oneanother, a loading/unloading station in which a clamping station islocated being provided next to that row of machine tools. In theclamping station, workpieces are inserted into workpiece holders whichare held by a pivot arm of a loading device.

After the workpiece holder has been loaded with a new workpiece, thepivot arm is pivoted in and the loading device travels to one of themachine tools, where the pivot arm pivots back out and the workpieceholder is clamped in a fixture holder which is provided in the workingspace of that machine tool. After machining of the workpiece, theworkpiece holder is transported either to another machine tool for afurther machining operation or back to the loading/unloading stationwhere the machine workpiece is replaced with a workpiece that is yet tobe machined.

The pivot arm of the loading device grasps the workpiece holder on oneside, the latter also grasping the workpiece to be machined on one side.The fixture holder in the working spaces also grasps the workpieceholder on one side; a buttress can selectably be provided so thatclamped workpieces can be better centered.

It has been found that with the known machining center, the handling ofthe workpieces and workpiece holders is disadvantageous particularlywhen bulky and/or heavy workpieces are to be machined. On the one hand,surprisingly, the machining accuracy and the reproducibility of themachining operation decrease when heavier and/or more bulky workpiecesare used. These disadvantages can be partially eliminated or at leastdiminished by performing workpiece handling in general at lowervelocities. This means, however, that in order to achieve high machiningaccuracy and reproducibility in the machining of heavy and/or bulkyworkpieces, the workpiece-to-workpiece time is reduced with the knownmachining center, which of course is disadvantageous.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toimprove the machining center mentioned at the outset in such a way thatenhanced machining speed and machining accuracy are achieved by means ofa simple design, in particular with heavy and/or bulky workpieces.

In the case of the machining center mentioned at the outset, this objectis achieved in that a multiple coupling for transferring fluidic energy,which is selectably docked in the clamping station, is provided on theworkpiece holder.

The object underlying the invention is completely achieved thereby.

Specifically, the inventors of the present application have recognizedthat the impairment in machining accuracy with heavy workpieces isattributable, inter alia, to the fact that the holding forces in theworkpiece holders are not sufficient, and further that the position ofthe workpieces cannot be sufficiently monitored. By means of themultiple coupling, fluidic energy can now be used on the one hand toactuate self-locking clamping elements and on the other hand tointerrogate back pressure sensors which indicate the position of theworkpiece via stops, etc. A considerable improvement in machiningaccuracy can be achieved by setting the workpieces in positionallyaccurate fashion into the workpiece holders, and optionally byincreasing the holding force in the working space; the self-lockingclamping elements allow rapid displacement of the loading device, thusalso increasing the machining speed.

It is preferred in this context if a cover for coupling elements of themultiple coupling is provided.

The advantage here is that the coupling elements cannot become soiledwhere they are not needed. This once again increases the machiningspeed, since it is not necessary to flush the coupling elements beforeusing the multiple coupling in order to ensure reliable operation. Thecover can, for example, be spring-loaded and self-closing, so that it isopened only when the multiple coupling is docked.

On the other hand, however, it is preferred if a handling system isprovided for removing and attaching the cover.

The advantage here is that reliable operation of the cover, which is notalways guaranteed with spring-loaded covers, is ensured. A high level ofreliability enhances the overall machining accuracy, since malfunctionsdue to soiled coupling elements as a result of covers which fail toclose are prevented.

It is further preferred in this context if the handling system isarranged on the loading device, and attaches and removes the covers asthe tool holder is being transported.

This feature is advantageous in terms of design on the one hand becauseit dispenses with a handling system in each working space. It may benoted here that the coupling elements need to be covered in particularin the working space, where on the one hand they are not needed, and onthe other hand a particular risk of soiling exists. It would thus beconceivable to provide in each working space a separate handling systemhaving its own cover which protects the unnecessary coupling elements. Asimpler design, on the other hand, would be to provide only one handlingsystem in the clamping station, in which the cover is in each caseremoved from the multiple coupling before use, and later attached again,so that each fixture has its own cover. The time saving with thisapproach is not yet sufficient, however, since in this case the removaland attachment of the cover further increases the workpiece-to-workpiecetime. If, however, the handling system is now arranged on the loadingdevice, the cover can be attached or removed simultaneously withdisplacement of the loading device between the working space andclamping station, so that the workpiece-to-workpiece time does notchange as a result of this cover handling.

It is further preferred in this context if, for transporting theworkpiece holder, the loading device has a pivot arm which pivots induring displacement of the loading device and for workpiece changing ispivoted into the working space or into the clamping station; and if thehandling system is arranged on a support part for the pivot arm in sucha way that when the pivot arm is pivoted in, the multiple coupling endsup located opposite the handling system.

This feature is advantageous in terms of design: the handling systemneeds only to perform a linear movement toward or away from the multiplecoupling and grasp the cover in order to pull it off, or release it sothat it can be pivoted into the working space together with the multiplecoupling.

It is preferred in general if the workpiece holder comprises a fixturehaving self-locking clamping elements for positionally accurate clampingof a workpiece, the fixture comprising a coupling module for supplyingthe clamping elements with fluidic energy.

This feature makes it possible once again to increase the machiningaccuracy appreciably, since part of the accuracy loss with heavierworkpieces in the prior art is attributable to the fact that theseworkpieces are not held securely enough in the workpiece holder. By wayof the coupling module, the clamping elements are now supplied withfluidic energy both in the clamping station and in the working space, sothat the workpieces can be held securely during both machining andpositioning. The coupling module moreover makes it possible to useself-locking clamping elements whose clamping force in the working spaceis enhanced by the fluidic energy and which can be actively opened inthe clamping station. These self-locking clamping elements hold theworkpieces so securely during transportation between the clampingstation and the working space that they can be moved and displaced veryquickly without changing their position in the mechanism.

While the multiple coupling is used only in the clamping station and,according to the present invention, is covered in the working space, thecoupling module is used in the above context both in the clampingstation and in the respective working space. The multiple coupling makespossible controlled clamping of the workpieces into the clampingelements. This is because the multiple couplings can make pneumaticconnections so that back-pressure metering can be used to monitor stops,etc. which indicate accurate placement of the workpieces. Because thismultiple coupling is coupled on selectably only in the clamping station,it is possible when the multiple coupling is open, both in the workingspace and in the clamping station, to rotate the fixture via a rotarydistributor which comprises only the coupling module that is requiredfor clamping the clamping elements. The large number of couplingelements required for the back-pressure metering, etc. can be providedin the multiple coupling, the mating element of which is necessary onlyin the clamping station, resulting overall in design advantages for thenew machining center.

It is preferred in this context if the fixture has on at least one ofits end faces a holding part with which it is clamped into a buttress inthe clamping station and in a working space, there being preferablyprovided on the buttress a docking mechanism, having coupling elementsand being associated with the multiple coupling, which is displaceableindependently from the buttress in terms of opening and closing themultiple coupling.

This feature is also advantageous in terms of design, since opening andclosing of the multiple coupling in the clamping station areaccomplished via a simple linear movement, and can thus be performedvery quickly.

It is further preferred if the multiple coupling has a support platearranged on one end face and equipped with coupling elements, and if thedocking mechanism comprises a carriage equipped with associated couplingelements, a locking unit being provided between the support plate andcarriage.

This locking unit ensures that the multiple coupling is securely coupledin, and thus guarantees reliable control signals and measurementsignals, which generally improve machining accuracy and machining speed.

It is further preferred if the cover comprises receiving orifices forcoupling elements of the support plate, one of the receiving orificeshaving a ball-spring catch which snap-locks onto a coupling element.

The advantage here is that the cover on the one hand receives all thecoupling elements in receiving orifices, i.e. encloses them inprotective fashion, the cover being retained on the multiple couplingvia a ball-spring catch, i.e. not requiring active actuation.

It is preferred in this context if the handling system comprisesactively opened gripper jaws.

The advantage here is that a handling system having actively openedgripper jaws allows very reliable attachment and removal of the cover.

Further advantages are evident from the description and the appendeddrawings.

It is understood that the features mentioned above and those yet to beexplained below can be used not only in the respective combinationsindicated, but also in other combinations or in isolation, withoutleaving the context of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is shown in the drawings and will beexplained in more detail in the description below. In the drawings:

FIG. 1 shows a partial frontal view of the new machining center;

FIG. 2 shows a section through the machining center of FIG. 1 along lineII—II, without the loading device in the loading space;

FIG. 3 shows a section along line III—III of FIG. 1, with the loadingdevice in position and the pivot arm swung in;

FIG. 4 shows a depiction like FIG. 3, but with the pivot arm swung out;

FIG. 5 shows, in an enlarged side view, the clamping station of the newmachining center with a fixture which receives workpieces to be machinedand can be clamped between a fixed and a movable buttress but is notcarried by gripper hands;

FIG. 6 shows a depiction like FIG. 5, but with the fixture clampedbetween the movable and the fixed buttress;

FIG. 7 shows a depiction like FIG. 6, but with the multiple couplingdocked in;

FIG. 8 shows a plan view of the end face of the fixture of FIG. 5 whichfaces toward the movable buttress, with a support plate for the multiplecoupling;

FIG. 9 shows a plan view of the movable buttress of FIG. 5 with thedocking system;

FIG. 10 shows a depiction of the upper region of the loading device withpivot arm and double gripper, in a depiction like FIG. 2, i.e. on theside facing the movable buttress;

FIG. 11 shows, in a schematic depiction, a view of the loading device inthe direction of arrow XI of FIG. 10;

FIG. 12 shows a plan view of the cover of the fixture of FIG. 10; and

FIG. 13 shows a schematic side view of the handling system of FIG. 11.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows, in a frontal view, a machining center 10 in which machinetools 11, 12, and 13 (merely indicated) are arranged next to oneanother. In addition to machine tools 11, 12, and 13, aloading/unloading station 14 is provided.

Machine tools 11, 12, 13 have an enclosure 15 which surrounds themcompletely and in which an operator door 16, through which an operatorgains access to a working space 17, is provided for each machine tool11, 12, 13. Retooling and service operations are performed for theindividual machine tools 11, 12, 13 through this operator door 16.

A clamping station 18 (indicated merely schematically), in whichindividual workpiece holders 19 are equipped with workpieces 21 to bemachined, is provided in loading/unloading station 14. Workpiece holders19 equipped in this manner with workpieces 21 are transported by meansof a loading mechanism 22 to the individual machine tools 11, 12, 13,and there inserted into the respective working space 17 and machined.Once machined, workpieces 21 are transported with their workpieceholders 19 out of working spaces 17 back to clamping station 18, wherethey are exchanged for new workpieces 21 to be machined.

It is further evident from FIG. 1 that an operating console 23, viawhich the usual operator inputs can be made, is provided at each machinetool 11, 12, 13 and at loading/unloading station 14.

With the new machining center 10 of FIG. 1, loading mechanism 22 isarranged in a loading space 25 which is located beneath working spaces17 of machine tools 11, 12, 13 and preferably inside enclosure 15. Inthis loading space 25, a loading device 26 runs back and forth along aguide rail 27 and thereby transports workpiece holders 19, containingworkpieces 21, between clamping station 18 and working spaces 17 orbetween individual working spaces 17 of different machine tools 11, 12,13.

FIG. 2 shows, in a partial sectioned depiction along line II—II of FIG.1, a cross section through machine tool 12, indicating a spindle head 29which is provided for machining workpieces in working space 17.

Machine tool 12 comprises a machine base 31 on which is provided aschematically indicated workpiece table 32, which, so to speak, spans aworking surface 33 in working space 17. Arranged on workpiece table 32is a fixture holder 34 which, as a fixed buttress, is equipped to graspworkpiece holder 19 and hold it during machining with tools provided inspindle head 29. In FIG. 2, 19′ designates a workpiece holder whichholds an already machined workpiece, workpiece holder 19′ being merelyindicated by a circle.

Loading space 25 is connected to working space 17 through a loadingopening 36. In this context, a cover 37 is provided which is closedwhile the workpieces are being machined with tools in working space 17,so that contaminants do not get into loading space 25.

Cover 37 is configured in two parts, and comprises a sliding cover 38which faces upward in FIG. 2 and is inclined toward working surface 33,as well as a swing-out cover 39 which extends approximatelyperpendicular to working surface 33 and can be swung toward it. It isevident that sliding cover 38 overlaps swing-out cover 39, so thatsplashes of cutting fluid, flying workpiece chips, etc. also cannot passthrough between sliding cover 38 and swing-out cover 39 into loadingspace 25.

FIG. 3 shows, in a depiction similar to that of FIG. 2 but along lineIII—III of FIG. 1, the situation in which cover 37 is open and loadingdevice 26 has been moved into the region beneath working space 17 of, inthis case, machine tool 11.

This loading device 26 is, so to speak, a self-displacing workpiecechanger 40 which has a drive unit 41 with motor 42, engaging on guiderail 27, which ensures in suitable fashion that loading device 26 cantravel along guide rail 27 which is preferably profiled in crosssection.

The displaceable workpiece changer 40 furthermore has a pivot arm 43swingably attached thereto, which in FIG. 3 is swung in so that it islocated in loading space 25. Arranged at the upper end of pivot arm 43is a rotatable double gripper 44 which carries on its one hand aworkpiece holder 19, while the other hand is still unoccupied.

Also evident from FIG. 3 is an ordinary trailing cable installation 45which makes available electrical, pneumatic, and (if necessary)hydraulic connections 46 for loading device 26 and connects the lattervia said connections 46 to the associated control unit/operator console23.

Also evident from FIG. 3 is a workpiece table 47, arranged behindswing-out cover 39, which carries a movable buttress 48 that isdisplaceable on rails 50 by means of a motor 49 in order better tocenter workpiece holder 19.

In the depiction of FIG. 4, which otherwise corresponds to FIG. 3, pivotarm 43 has been pivoted or extended through loading opening 36 intoworking space 17, where double gripper 44 has already gripped workpieceholder 19′ which carries a workpiece that has already been machined bymachine tool 11. Workpiece holder 19 and workpiece holder 19′ are nowexchanged by way of a pivoting movement through 180 degrees in the planeof FIG. 4, so that fixture holder 34 evident in FIG. 2 can pick upworkpiece holder 19 with the workpiece that is yet to be machined. Pivotarm 43 is thereupon swung or pulled back in, so that it assumes theposition shown in FIG. 3.

Lastly, cover 37 is closed so that machining of the new workpiece can beaccomplished in working space 17 of machine tool 11, while loadingdevice 26 brings workpiece holder 19′ to a further machine tool or toloading/unloading station 18 and there exchanges it for a workpieceholder 19 that was equipped in clamping station 18 with a workpiece thatis yet to be machined.

In FIG. 5, clamping station 18 is shown in enlarged and more detailedfashion. Serving as workpiece holder 19 here, according to the presentinvention, is a fixture 51 similar to a cradle plate, which has on itsbottom plate 52 self-locking clamping elements 53 in order to clamp inworkpiece 21 (indicated schematically) at both ends. By way of theselection of the length and width of bottom plate 52, fixture 51 canreceive workpieces 21 of any bulk, since because of clamping elements53, preferably located opposite one another, even very heavy workpieces21 can be held securely.

Fixture 51 furthermore has two end plates 54 and 55, each joined tobottom plate 52, on each of which a hollow shaft taper 56 and 57 knownper se, having the usual gripper groove, is provided. Hollow shafttapers 56, 57 of this kind are used, inter alia, as tool holders inautomatic tool changing systems.

In FIG. 5, 58 and 59 schematically indicate two gripper hands which holdfixture 51 in accurately positioned fashion between fixed buttress 35and movable buttress 48. A hollow shaft taper (HSK) receptacle 60 havingthe usual clamping set is provided on fixed buttress 35, an HSKreceptacle 61 with the usual clamping set also being provided on movablebuttress 48. Just like HSK receptacles 60 and 61, HSKs 56 and 57 serveas holding parts 62 by means of which fixture 51 is immovably clampedinto clamping station 18. For this purpose, gripper hands 58, 59 movefixture 51 in the direction of an arrow 63 so that HSK 56 is clampedinto HSK receptacle 60. Movable buttress 48 is thereupon moved by motor49, on rails 50, to the left in the direction of an arrow 64, until HSK57 is clamped in HSK receptacle 61.

Arranged beneath HSK 57 is a coupling module 66 which carries a couplingelement 67 that coacts with a coupling element 68 on movable buttress 48so that fluidic energy is delivered to fixture 51 via a line 69 toactuate clamping elements 53. By way of this fluidic energy, which isgenerally supplied on a hydraulic basis, workpieces 21 can be clampedinto fixture 51 and released from it. Clamping elements 53 areself-locking, so that the position of workpiece 21 does not change whilefixture 51 is being transported by loading device 26.

In addition to coupling module 66, which is used both in clampingstation 18 and in the respective working space 17 of a respectivemachine tool 11, 12, or 13, fixture 51 also has a multiple coupling 70which is used only in clamping station 18.

This multiple coupling 70 comprises a support plate 71, attached to endplate 55, on which multiple coupling elements 72 are provided, of whichonly one is shown schematically in the side view of FIG. 5.

Support plate 71 coacts with a docking system 73 which carries acarriage 74 that can be displaced to the left in FIG. 5 via a motor 75.Coupling elements, corresponding to coupling elements 72 and not visiblein the depiction of FIG. 5, are provided on carriage 74.

Via multiple coupling 70, hoses 76 are supplied with compressed airwhich is used for pneumatic back-pressure metering. For example, hose 76a is connected to clamping element 53 and provides position monitoringfor workpiece 21.

Multiple coupling 70 makes available functions for fixture 51 whichconcern correctly positioned clamping of workpieces 21 and are thusrequired only in clamping station 18. A movable buttress 48 is alsoprovided in machine tools 11, 12, 13, but without a docking system 73.

FIG. 6 shows, in a depiction like that of FIG. 5, the situation in whichfixture 51 is clamped in immovably between fixed buttress 35 and movablebuttress 48, but docking system 73 has not yet coupled on.

In this state, fixture 51 can pivot back and forth about its pivot axis78 in the direction of a double arrow 79. Coupling module 66 that isalready coupled in does not interfere with this, since it coacts with arotary distributor on movable buttress 48, as will be explained later inconnection with FIG. 9.

Pivoting of fixture 51 in clamping station 18 is necessary on the onehand so that fixture 51 can be flushed and blown clean from all sides,i.e. so that chips and adhering cutting fluid can be removed from aworkpiece 21 that has already been machined. In addition, fixture 51itself is also correspondingly cleaned after removal of the machinedworkpiece 21.

Fixture 51 is designed to carry even very bulky and/or heavy workpieces;depending on the geometrical arrangement, these workpieces can beremoved from or inserted into a fixture 51 that has pivoted about pivotaxis 56 out of the horizontal position shown in FIG. 6. For thisworkpiece change, however, clamping elements 53 shown in FIG. 5 must becapable of being actuated even in the tilted position, which is why thehydraulic power supply of hose 69 is provided via the rotary distributoralready mentioned.

It may be noted here that a rotary distributor of this kind is alsopresent in the machine tool. While the clamping force of theself-locking clamping elements 53 is great enough to ensure thatworkpiece 21 maintains its position while fixture 51 is beingtransported by loading device 26, the holding force is not, however,sufficient to hold workpiece 21 in position during machining. For thispurpose, a hydraulic power supply is again provided via hoses 69. Sincefixture 51 must be pivoted in the manner of a cradle plate duringmachining, movable buttress 48, which is provided in each machine tool11, 12, 13, also contains a rotary distributor as described below inconnection with FIG. 9.

FIG. 7 shows, in a depiction like that of FIG. 6, a situation in whichmotor 75 has pushed carriage 74 of docking system 73 to the left, sothat the coupling elements on carriage 74 now come into engagement withcoupling elements 72 on support plate 71. One coupling element 81 isshown, by way of example, on carriage 74.

FIG. 8 shows a plan view of end plate 55 of fixture 51 in the directionof arrow VIII of FIG. 5. It is evident that support plate 71 comprises atotal of fourteen coupling elements 72 for compressed air, two couplingelements 82 for hydraulics and one plug part 83 for a locking unitfurthermore being provided.

Coupling module 66 beneath HSK 57 comprises three coupling elements 67for hydraulics; these coupling elements 67 are also used in machinetools 11, 12, 13, while multiple coupling 70, as already mentionedseveral times, is utilized only in clamping station 18.

Also shown in addition to HSK 57, as the positioner part, is a centeringpin 84 via which pivoting of fixture 51 and positionally accuratecoupling are effected, in order to prevent shear forces on couplingelements 67.

FIG. 9 shows, in a manner complementary to FIG. 8, a plan view ofmovable buttress 48 in the direction of arrow IX of FIG. 5. Carriage 74is mounted via rails 85, displaceably perpendicular to the drawing planeof FIG. 9, on buttress 48 which is itself displaceable. FIG. 9 showsthat carriage 74 carries coupling elements 86 for hydraulics that arecomplementary to coupling elements 82, as well as a socket part 87 whichtogether with plug part 83 on support plate 71 constitutes a lockingunit by means of which multiple coupling 70 is reliably positioned andlocked when carriage 74 is moved toward support plate 71.

While carriage 74 is present only on movable buttress 48 in clampingstation 18, the remainder of buttress 48 that will now be describedcorresponds to the one also used in machine tools 11, 12, 13.

Movable buttress 48 contains a rotary distributor plate 88 which isguided, pivotably in the direction of arrow 79, in a circular guide 89.In addition to HSK receptacle 61 and coupling elements 68 associatedwith coupling elements 67, rotary distributor plate 88 also carries, aspositioner part, a receptacle 90 for centering pin 84 which is arrangedon end plate 55.

By the coaction of HSK 57 and HSK receptacle 61 on the one hand, and ofcentering pin 84 and receptacle 90 on the other hand, fixture 51 iscentered with reference to rotary distributor plate 88; when a rotationof rotary distributor plate 88 occurs about pivot axis 78, the pivotforce is transferred via centering pin 84 and receptacle 90 to fixture51, thus preventing shear forces on coupling elements 67, 68.

Docking system 73, which is displaceable independently of movablebuttress 48, thus makes available in clamping station 18 fourteenpneumatic connectors as well as two further hydraulic connectors,through which, when fixture 51 is in the horizontal orientation shown inFIG. 5, 6, or 7, the latter can be supplied with further functions orinquiries. When docking system 73 is not docked on or not present,fixture 51 can be pivoted via rotary distributor plate 88, the necessaryhydraulic connectors for releasing, closing, and holding clampingelements 53 being made available via coupling elements 67, 68.

FIG. 10 shows a fixture 51 which has been gripped by a loading device 26and pivoted into loading space 25. FIG. 10 shows a plan view of fixture51 which corresponds to the view of FIG. 8.

In the highly simplified depiction of an upper region of loading device26, a support part 92 of loading device 26 is shown in truncated fashionand also simply with dashed lines, in order to make fixture 51 visible.

Mounted firstly on support part 92 is pivot arm 43, which can be pivotedabout a pivot axis 93. Mounted at the other end of pivot arm 43,rotatably about a rotation axis 94, is double gripper 44 which comprisesboth gripper hand 58 that carries mechanism 51 and a free gripper hand58′. A catch pawl 95, which in the case of gripper hand 58 is extendedand holds HSK 57 in gripper hand 58, is provided on each gripper hand.On gripper hand 58′, catch pawl 95 is retracted so that after pivot arm43 has pivoted out and double gripper 44 has rotated correspondingly,this gripper hand 58′ can remove a fixture from a working space of amachine tool.

The drive system required for this purpose comprises on the one hand apivot motor 96 which drives, via a toothed belt 97, a gear 98 that isjoined to pivot arm 43 and sits on pivot axis 93. Pivot motor 96 ismoreover joined via a second toothed belt 99 to a gear 100 which sitsnonrotatably on a coupling rod 101 via which, in a manner yet to bedescribed, a pivot arm parallel to pivot arm 43 is driven separately. Itmay also be noted that pivot motor 96 of course has its own gear 102 onwhich the two toothed belts 97 and 99 are arranged next to one another.

Arranged concentrically in pivot axis 93 is a rotation motor 103 whichdrives, via a toothed belt 104, a gear 105 that is joined nonrotatablyto double gripper 44. The arrangement of rotation motor 103 on pivotaxis 93 makes it possible for double gripper 44 to be drivenindependently of the particular location of pivot arm 43.

FIG. 10 further shows that support plate 71 of fixture 51 is equippedwith a cover 106 for covering purposes, associated with which is ahandling system 107 (indicated only schematically).

In FIG. 11, which is a schematic view along arrow XI of FIG. 10, thishandling system 107 is shown in more detail at lower right; it isevident there that a drive unit 108 for handling system 107 is attachedon support part 92 of loading device 26. In the pivoted-in state, asshown in FIGS. 10 and 11, support plate 71 is located directly in frontof handling system 107, so that the latter must only perform a linearmovement in order to remove cover 106 or put it in place. The purpose ofcover 106 and the function of handling system 107 will be explainedbelow in connection with FIGS. 12 and 13.

It is evident from the upper part of FIG. 11 that a further doublegripper 44′ is provided parallel to double gripper 44, the two doublegrippers being at a distance from one another which allows them to graspa fixture 51 with their respective gripper hands 58, 58′ at HSKs 56, 57provided for the purpose; catch pawl 95, shown only on double gripper44, ensures that fixture 51 is held in lossproof fashion.

The two double grippers 44, 44′ are nonrotatably joined to one anotherby way of a rigid shaft 110, so that, so to speak, both double grippers44, 44′ are driven, thus preventing any tilting of fixture 51 whendouble grippers 44, 44′ are rotated about rotation axis 94.

The parallel double gripper 44′ sits on a further pivot arm 43′ which isarranged and driven parallel to pivot arm 43. This parallel drive isaccomplished via coupling rod 101 on which, remote from gear 100, theresits a further gear 111 which is in engagement via a toothed belt 112with a gear 113 that in turn is joined nonrotatably to a shaft 114 bymeans of which pivot arm 43′ is rotatable.

It is also evident from the right side of FIG. 11 that rotation motor103 extends with its motor shaft 115 through hollow gear 98. Motor shaft115 carries at its outer end a gear 116 which is in engagement, viatoothed belt 104, with gear 105 which in turn is joined nonrotatably toa shaft 117 which is attached on rigid shaft 110.

Pivot motor 96 thus drives both pivot arms 43, 43′ synchronously, sothat even with very heavy or bulky workpieces, fixture 51 can be pivotedquickly and reliably out of loading space 25 into working space 17 orinto clamping station 18. As a result of the rigid connection betweenthe two double grippers 44, 44′ via shaft 110, rotation of doublegrippers 44, 44′ is also accomplished synchronously, so that fixtures 51can be changed very quickly. The result of this highly rigid system isto prevent the occurrence of vibrations during the pivoting and rotationof fixtures 51 because of the large masses being moved; these vibrationsmust be allowed to decay before fixture 51 can be clamped between fixedbuttress 35 and movable buttress 48. Because these vibrations areabsent, not only can the fixtures be exchanged more quickly, butworkpieces 21, which are held only by the self-locking clamping elements53 while fixtures 51 are being transported, are also held more securelyin position, so that machining accuracy is increased in particular forthose workpieces which must be machined successively by multiple machinetools 11, 12, 13. The position of workpieces 21 on fixture 51 does notchange between the individual clampings in working spaces 17 of machinetools 11, 12, 13, since they are being moved very quickly but alsowithout vibration or shock.

Lastly, FIG. 12 again shows cover 106, already known from FIGS. 10 and11, for support plate 71, FIG. 12 being a plan view of the side of cover106 facing toward support plate 71. Cover 106 has receiving orifices 118for coupling elements 72, receiving orifices 119 for coupling elements82, and a receiving orifice 120 for plug part 83 of the locking unit.Also provided on the upper and lower edges of cover 106 are holdinggrooves 122, 123 which come into engagement with jaws 124, 125 ofhandling system 107, as shown in FIG. 13.

It is evident from the sectioned depiction of FIG. 13 that at least oneball-spring catch 126, by way of which cover 106 snap-locks onto plugpart 83, is provided in receiving orifice 120.

Jaws 124, 125 are attached to a pneumatically actuated gripper 128 ofhandling system 107, which in turn is guided displaceably, via a guiderod 129, on carrier part 92 of loading device 26. From drive unit 108,an actuation rod 130 passes into gripper 128. In a manner known per se,the arrangement is such that prior to an actuation of drive unit 108,jaws 124, 125 are first opened pneumatically, and then gripper 128 ispulled to the right in FIG. 13 via actuation rod 130; as a result, cover106 is released and remains on support plate 71 when fixture 51 ispivoted into working space 17 of a machine tool 11, 12, 13.

Cover 106 now protects multiple coupling 70 from soiling in workingspace 17 of a machine tool 11, 12, 13.

When fixture 51 is, on the other hand, to be pivoted into clampingstation 18, cover 106 is pulled away from support plate 71 by handlingsystem 107 even as loading device 26 is being displaced, so that whenfixture 51 is pivoted into clamping station 18, multiple coupling 70 isexposed and docking system 73 can dock therein. Of course each fixture51 has its own cover 106 associated with it, carried by handling system107 only in clamping station 18. When fixture 51 has been loaded with anew workpiece and pivoted into loading space 25, handling system 107places cover 106 back onto support plate 71 while loading device 26 isbeing displaced to the first machine tool 11, 12, 13, so that noadditional machine time is required for setting cover 106 in place andremoving it.

Therefore, what I claim, is:
 1. A machining center, comprising: a numberof machine tools each having a working space for machining workpiecesclamped into a workpiece holder; a clamping station in which workpiecesto be machined are clamped into said workpiece holders; and a loadingdevice moving between said clamping station and said machine tools fortransporting said workpiece holders from said clamping station to theworking space of at least one of said machine tools, and vice versa;wherein a multiple coupling is provided on each workpiece holder fortransferring fluidic energy, said multiple coupling being selectivelydocked and only used in the clamping station, and wherein said multiplecoupling comprises coupling elements, and a cover is provided for saidcoupling elements.
 2. The machining center of claim 1 in, wherein ahandling system is provided for removing and attaching the cover.
 3. Themachining center of claim 2, wherein the handling system comprisesactively opened gripper jaws.
 4. The machining center of claim 3,wherein the handling system is arranged on the loading device, andattaches and removes the cover as the workpiece holder is beingtransported.
 5. The machining center of claim 4, wherein fortransporting the workpiece holder, the loading device has a pivot armwhich pivots in during displacement of the loading device and forworkpiece changing is pivoted into the working space or into theclamping station; and the handling system is arranged on a support partof the pivot arm in such a way that when the pivot arm is pivoted in,the multiple coupling is located opposite the handling system.
 6. Themachining center of claim 1, wherein the workpiece holder comprises afixture having self-locking clamping elements for positionally accurateclamping of a workpiece, the fixture comprising a coupling module forsupplying the clamping elements with fluidic energy.
 7. The machiningcenter of claim 6, wherein the fixture has on at least one of its endfaces a holding part with which it is clamped into a buttress in theclamping station and in a working space, respectively.
 8. The machiningcenter of claim 7, wherein there is provided on the buttress a dockingmechanism, having coupling elements and being associated with themultiple coupling, which docking mechanism is displaceable independentlyfrom the buttress in terms of opening and closing the multiple coupling.9. The machining center of claim 8, wherein the multiple coupling has asupport plate arranged on one end face and equipped with couplingelements, and the docking mechanism comprises a carriage equipped withassociated coupling elements, a locking unit being provided between thesupport plate and carriage.
 10. The machining center of claim 9, whereinthe cover comprises receiving orifices for coupling elements of thesupport plate, one of the receiving orifices having a ball-spring catchwhich snap-locks onto a coupling element.